246 OF THE INVOLUCRUM, 



the genera of umbelliferous plants, for 

 which purpose the latter deemed the part 

 jn question very important. But accord- 

 ing: to the laws which Linnaeus had laid 

 down, the parts of the flower and fruit 

 alone were to afford generic characters, 

 and the most sound botanists have ever 

 since kept to this rule, with infinite advan- 

 tage over less correct ones, however ready 

 to derive ideas respecting the natural habjt, 

 and secondary characters, of a genus, not 

 only from the inflorescence and bracteas, 

 but even from the leaves, stipulas, or other 

 parts. Linnaeus and Artedi, therefore, were 

 obliged to consider the involucra and invo- 

 lucella, the former accompanying the ge- 

 neral and the latter the partial umbels, as 

 a sort of calyx, and the umbel altogether as 

 one aggregate flower, composed of florets 

 united by a common radiated receptacle. 

 Consequently a cyme must be considered 

 in the same light; nor are reasons wanting 

 in support of this hypothesis, which we 

 shall consider after having first explained 

 all the parts of fructification. 



In Euphorbia, however, the term bractea 



